A temporal-spatial solar radiation model to improve scaling of biogenic emissions from a sparse Mediterranean pine/oak forest

The diurnal and seasonal emission course from plants is controlled by light and temperature. The pattern of light incident on a surface changes with t ime and space, which is most obvious in cast shadows. A complex GIS-based s olar radiation model (SORAM) which is not restricted to certain test sites was developed. It is used for the first time to scale up biogenic emissions . Our main interest is to evaluate the effects on the amount of biogenic vo latile organic compounds emitted caused by the 3-dimensional surface of eit her a canopy stand or a complex terrain. Therefore a digital elevation mode l represents the canopy surface of the St. Quercio pine/oak forest (Castelp orziano, Italy). Temperature values are linked to the radiation output. Thi s enables us to correct emission factors for light and temperature by using Tingey's (1980) and Guenther's (1993) emission algorithms. The methods are described and results presented for 26 May 1994 and 3 August 1994. The sea sonality in the amount and composition of emitted compounds is clearly show n for P. pinea. Representing the canopy stand by a pseudo-3-dimensional sur face instead of a surface with a constant height value reduces emission flu xes from Q. ilex by 40%. The "global" emission flux of the test site decrea ses by 20%. The results are compared with values derived from different mea surement techniques and upscaling methods. Suggestions are made to overcome the limitations of the pseudo-3-dimensional presentation of the canopy sta nd. (C) 1999 Elsevier Science Ltd. All rights reserved.